Use epicsFindSymbol() to build a dynamic and idempotent equivalent
to the code generated by registerRecordDeviceDriver.pl
Also add runRegistrarOnce() to prevent registrars
from running multiple times, except from unittest code.
In some cases the license-identification header was missing,
so I added that as well. Replaced the remaining headers that
specifically identified "Versions 3.13.7 and higher".
Makefiles and the build system were deliberately excluded.
